Engine exhaust systems have utilized hydrocarbon retaining devices, such as hydrocarbon traps, to retain cold start emissions for later reaction, or to recirculate into the engine intake system. In one particular example, the purging of exhaust gases may be enabled when the device reaches a predetermined temperature.
However, the inventors herein have recognized several issues with such examples. Specifically, the engine may operate with varying fuel compositions thereby producing exhaust emissions that may have different adsorption and/or desorption characteristics. For example, flex-fuel vehicles that operate on fuel having a varying alcohol composition (e.g., ranging from gasoline (E0) to ethanol (E85)) may have significantly different exhaust water content, thereby affecting the temperature at which exhaust constituents are stored and/or released. Further, different hydrocarbon chains may be produced in the exhaust depending on the fuel composition also having different storage/release characteristics. In one particular example, hydrocarbons may be trapped in an HC retaining device up to higher temperatures with increased alcohol content in the fuel. As such, an appropriate control to trapping tailored for combustion of one fuel composition may lead to breakthrough, or inefficient trapping, for combustion of a second fuel composition.
The above issues may be addressed by a method of operating an engine having an intake, an exhaust, and a hydrocarbon-retaining system, the engine combusting fuel, the method comprising: selectively routing exhaust gases of the engine to the hydrocarbon retaining system to store exhaust hydrocarbons; selectively purging stored hydrocarbons from the hydrocarbon retaining system to the engine intake; and varying an initiating of the selective purging of stored hydrocarbons responsive to a condition.
In one example, the purging can be adjusted to the particular fuel properties of the fuel combusted in the engine, such as the alcohol content of the fuel combusted in the engine. In this way, it is possible to adjust the purging to take advantage of the particular storage/release properties of the exhaust constituents particular to the combusted fuel alcohol content. This can increase the storage capacity utilization, as well as reduce breakthrough of the hydrocarbon-retaining system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.